1. Field of the Invention
The present invention relates to readable/writable information recording medium. More specifically, the present invention relates to an information recording medium for recording multimedia data in different kinds of formats such as movie image data, still picture data and audio data; and a data recording apparatus and replaying apparatus for the medium.
2. Related Art
Development of phase change type disc DVD-RAM has increased recording capacity of a rewritable optical disc from about 650 MB to a few GB. The DVD-RAM is now expected to become a medium not only for computers but also a recording/playing medium for audio/video (hereinafter abbreviated as AV) technologies in combination with standardization of a digital AV data coding technique called MPEG (MPEG2). Specifically, the DVD-RAM is expected to replace magnetic tape which has been a major AV recording medium.
(DVD-RAM)
Advancement in high-density recording technology for rewritable optical discs in recent years has made it possible to store not only computer data and audio data but also image data as well.
Conventionally, land and groove are formed on a signal recording surface of the optical disc.
Signals used to be recorded only on the land portion or in the groove portion. Later, land-group recording method was developed for recording signals both in the land portion and in the groove portion, practically doubling the recording density. For example, a technique disclosed in Japanese Patent Laid-Open Publication No. 8-7282 is well known.
Another of such techniques is CLV (Constant Linear Velocity recording) method for improving recording density. From this technique, zone CLV method was developed and is now commercially practiced for simplified control in application. Japanese Patent Laid-Open Publication No. 7-93873 is a known example of this technique.
With such development in the optical disc for greater recording capacity, a technological challenge is how to record AV data including image data, thereby achieving new performances and functions that have never been realized by prior art AV apparatuses.
The development of the large-capacity rewritable optical disc is expected to replace the conventional tape medium for recording/playing AV data. The change from tape to disc will bring substantial changes in the function and performance of the AV equipment.
The biggest change to be brought by the disc is tremendous improvement in random access capability. If tape is to be accessed randomly, rewinding time of the tape, which is usually a few minutes per reel, must be taken into account. Such an access time is extremely slower than a seek time (which is shorter than a few tens of millisecond.) for the optical disc. Thus, in a practical sense, the tape cannot be a random access medium.
Such a superb random access capability of the optical disc can realize distributed recording of AV data in the optical disc, which was not possible with the conventional tape medium.
Referring now to the attached drawings, FIG. 1 is a block diagram of a DVD recorder drive unit. The drive unit comprises an optical pickup 11 for reading data stored in a DVD-RAM disc 100, an ECC (Error Correcting Code) processor 12, a one-track buffer 13, a switch 14 for selecting between input and output to and from the track buffer 13, an encoder 15, and a decoder 16.
As shown in the figure, the DVD-RAM disc 100 uses one sector (1 sector=2 KB) as a smallest unit of data recording, and one ECC block (1 ECC block=16 sectors) is used as a unit for error correcting operation performed by the ECC processor 12.
The track buffer 13 is a buffer for storing AV data at a variable bit rate to record AV data effectively in the DVD-RAM disc 100. Specifically, reading/writing for the DVD-RAM 100 is performed at a fixed rate (Va), whereas the bit rate (Vb) of AV data is varied according to complexity of contents (e.g. an image for video data). The buffer 13 absorbs difference between these two bit rates. When the AV data have a fixed bit rate such as in a video CD, then the track buffer 13 is not required.
If this track buffer 13 is used more effectively, distributed recording of AV data on the disc 100 becomes possible. This will be described more specifically here below, referring to FIGS. 2A and 2B.
FIG. 2A is a diagram showing address space on the disc. According to FIG. 2A, AV data is stored in a distributed manner, i.e. in a continuous area [a1, a2] and in another continuous area [a3, a4]. In such a case, the AV data can be replayed continuously supplying data stored in the buffer 13 to the decoder portion 16 while seek is being made from point a2 to point a3. This situation is shown in FIG. 2B.
The AV data starting from the location al are read, and then entered to the track buffer 13 from time t1, upon which time the track buffer 13 begins to output the data. Thus, the buffer 13 accumulates data at a rate equal to the difference (Va-Vb) between the input rate (Va) to the buffer 13 and the output rate (Vb) from the buffer 13. This situation continues until the retrieval reaches a2 represented by a time point t2, by which time the amount of data in the buffer 13 has accumulated to amount B(t2). From time t2 to time t3, until the data pickup operation is resumed from the area starting at a3, the amount of data B(t2) stored in the track buffer 13 is being consumed in order to keep the decoder 16 supplied with data.
In other words, when the amount of data ([a1, a2]) read before the seeking is greater than a certain volume, then the AV data can be continuously supplied without being interrupted by the seek.
The above description is for reading of data from the DVD-RAM, i.e. for a play back operation. The same goes with writing data to the DVD-RAM, i.e. for a recording operation.
As described above, with the DVD-RAM, continuous replaying/recording is possible even if AV data is stored in the distributed manner, as long as the amount of data on each continuous record is greater than a certain volume.
In order to enhance advantages of the large-capacity recording medium, i.e. DVD-RAM, a UDF (Universal Disc Format) file system is used in the DVD-RAM as shown in FIG. 3 to allow access to the disc by using a PC. UDF information is recorded in "Volume" area of the diagram. Details of the UDF file system is disclosed in the "Universal Disc Format Standard."
(Prior-art AV equipment)
Next, description will be made for prior art AV equipment commonly used by many users.
FIG. 4 is a diagram showing relationships among conventional AV equipment, media and formats. For example, if a user wants to watch a video program, a videocassette must be loaded into a VTR, and the program must be viewed using a TV set. If the user wants to listen to music, then a CD must be loaded into a CD player or CD radio-cassette player, and the program must be listened through a speaker system or through headphones. Specifically, according to the conventional AV system, each format (video or audio) is paired with a corresponding medium, respectively.
For this reason, each time when listening or watching a program, the user must select an appropriate medium and change one to another AV equipment appropriate to the medium. This is inconvenient from the user's viewpoint.
(Digitization)
Meanwhile, along with recent popularization of digital technology, a DVD videodisc was introduced as package software, whereas satellite digital broadcast was introduced in the broadcasting industry. These developments are backed by digital technology innovation, especially by MPEG as an internationally accepted standard.
FIG. 5 is a diagram showing MPEG streams used in the DVD videodisc and the satellite digital broadcast mentioned above. The MPEG standard has a hierarchy structure as shown in FIG. 5. An important point to note here is that the MPEG stream eventually used by an application in the package medium such as the DVD videodisc is different from the MPEG stream in the communication medium such as the satellite digital broadcasting. The former is called "MPEG program stream", in which data transfer is made by the unit of pack, reflecting the size of a sector (2048 bytes in DVD video disc) as the unit of recording in the package software. On the other hand, the latter is called "MPEG transport stream", in which the unit of data transfer is a TS packet having a size of 188 bytes, reflecting the application to ATM (Asynchronous Transfer Mode) systems.
The MPEG is expected to eliminate borders between different AV media, as a universal coding technology of image signals and digital data. However, because of such small differences as described above, there is not yet any AV equipment or media capable of handling both the package media and communication media.
(Changes Brought by DVD-RAM)
Introduction of the large capacity DVD-RAM is a step forward to elimination of the inconvenience that users feel in conventional AV equipment. As described earlier, the DVD-RAM incorporated with the UFD file system is accessible from the PC. By using different pieces of application software on the PC, it is now possible to play varieties of contents such as video, still picture and audio programs on a single piece of equipment, i.e. the PC.
As shown in FIG. 6, the user can move a cursor with a mouse onto a file displayed on a screen, and then double-click (or single-click) to replay contents of the file such as a movie displayed in left-top area of the screen.
Such a convenience becomes possible by combination of flexibility offered by the PC and large storage capacity offered by the DVD-RAM.
Backed by increasing popularity of the PC in recent years a number of different AV data can now be handled fairly simply on the PC as shown in FIG. 6. However, even though number of PC users is expected to increase, the popularity and easiness of operation of the PC are not so high and simple as those of the home TV or home video systems.
It is therefore an object of the present invention to solve the following problems identified as hurdles to optimum performance of the optical discs such as the DVD-RAM, as an AV recording medium of the next generation.
A world to be realized by the DVD recorder would be a world in which the user can freely handle different formats and contents without caring about the differences, by using a single medium on a single piece of AV equipment as shown in FIG. 7.
FIG. 8 shows an example of a menu used in the DVD recorder. According to this menu, the user can select from 1) "The Foreign Movie Theater" recorded from satellite digital broadcasting, 2) "The Morning Drama Series", 3) "The World Cup Finals" each recorded from conventional terrestrial broadcasting, and 4) a Beethoven dubbed from a CD, on a TV screen without caring about the original medium or the recording format.
The biggest problem in developing such a DVD recorder as above is how to manage uniformly the AV data and streams of many different formats.
No special managing method will be necessary if only a limited number of existing formats are to be handled. However, a managing method capable of handling not only a number of existing formats but also new formats to be introduced in the future has to be developed in order to realize the above-mentioned world of DVD recorder.
Even so, certain difference between a future user interface and those incorporated in the capability of uniformly handling the different AV streams may create a certain level of inconvenience similar to the inconvenience described for the prior-art. Specifically, the user may have to perform different operation depending upon the contents or format.